Degassing system for a hydrocarbon dispenser

ABSTRACT

A degassing system for a hydrocarbon dispenser including a hydrocarbon circulating pump (12). The system includes a degassing assembly (16) having an inlet connected to the outlet of the pump, a degassed hydrocarbon outlet (90), a takeoff outlet (20) for taking off the hydrocarbon/gas mixture, a degassing vessel (24), and a duct (38, 60&#34;) for connecting the takeoff outlet to the degassing vessel. The end of the duct which opens out into the degassing vessel has an adjustable effective flow section. The system also includes a valve arrangement (110, 118) for modifying the effective flow section as a function of the gas content of the hydrocarbon.

BACKGROUND OF THE INVENTION

The present invention relates to a degassing system for a hydrocarbondispenser.

In hydrocarbon dispensers, it is known that it is necessary to degas thehydrocarbon in order to ensure that the volume of hydrocarbon deliveredto a user does indeed correspond to hydrocarbon and not to a volumemixture of liquid hydrocarbon plus gas.

In European patent No. 0 357 513, a hydrocarbon dispenser is describedthat includes means for monitoring the gas content of the hydrocarbon.In that document, the hydrocarbon dispenser is provided with a vortextype degasser which is associated with detection means enablinghydrocarbon dispensing to be interrupted as soon as the gas contenttherein exceeds a predetermined value. Vortex degassers are commonlyused in that type of installation. They consist in establishing ahelical flow of liquid-and-gas mixture in an elongate cylindricalenclosure, in taking off the liquid-enriched fraction via a lateraltube, and in taking off a gas-enriched fraction via an axial tube.

Accompanying FIG. 1 is a diagram showing a degassing device as commonlyused in hydrocarbon dispensers. In this figure, a pump 12 is showncausing hydrocarbon to pass from a storage tank 14 to a vortex degasser16 which is constituted by an elongate cylindrical enclosure, asmentioned above. The hydrocarbon, possibly containing gas, is injectedto a first end of the enclosure 16 by duct 18 in such a manner as toestablish helical motion of the hydrocarbon inside the enclosure 16.Degassed hydrocarbon is taken via lateral duct 22 while a liquidfraction that is possibly enriched in gas is taken via axial duct 20.Exit tube 20 is connected to a duct 26 which is in turn connected to adegassing tank or vessel 24.

Looking at the device of FIG. 1, it will be understood that one of theproblems associated with such a system is that in the most usualsituation of the gas content being very low, the axial takeoff tube 20is in fact going to take off a non-negligible quantity of hydrocarbon,possibly containing very little gas. It will be understood that thishydrocarbon which is transferred to the degassing vessel reduces theeffective efficiency of the installation since this hydrocarbon fractionmust be recycled to the inlet of the pump 12 after spending a length oftime in the vessel 24.

In contrast, it will be understood that when, accidentally, thehydrocarbon happens to have a high gas content, it is necessary toprovide a takeoff tube 20 of diameter that is sufficient to take offeffectively the entire gas-filled hydrocarbon fraction.

Also known, from U.S. Pat. No. 2,779,503, is a degassing system of thetype shown in FIG. 1, in which the end of the duct opening out in thedegassing vessel carries a non-return valve of effective through sectionthat is adjustable by the action of a float resting on the liquidcontained in the vessel. When the liquid content is large in theliquid/gas mixture taken off at the outlet from the degassing enclosure,the vessel fills with liquid, thus having the effect of raising thelevel of the liquid in the degassing vessel, and thus closing thesection of the valve. Conversely, if the mixture taken off is rich ingas, then the level of liquid in the vessel remains substantiallyconstant and the valve remains open to pass gas.

However, it can be observed that the above-known degassing system has aresponse time that is relatively long since when the liquid/gas mixturebecomes enriched in liquid it is necessary to allow enough liquid topour pointlessly into the degassing vessel to cause the liquid level torise far enough to cause the valve to move through its entire strokefrom its open position to its closed position.

SUMMARY OF THE INVENTION

To remedy the above drawback, the invention proposes a degassing systemfor a hydrocarbon dispenser having a pump for making hydrocarbon flow,said system comprising a degassing assembly having an inlet connected tothe outlet of the pump, and a degassed hydrocarbon outlet, and a takeoffoutlet for taking off a hydrocarbon/gas mixture, a degassing vessel, andduct-forming means for connecting said takeoff outlet to said degassingvessel, the end of said duct-forming means opening out into saiddegassing vessel having an effective flow section that is adjustable,the system being remarkable in that it further includes pressure meansfor modifying said effective flow section as a function of the gascontent of the hydrocarbon in the degassing assembly.

It will be understood that because of this disposition of the invention,when the gas content is very low, hydrocarbon takeoff is kept low byreducing the effective flow section of the duct-forming means. Incontrast, when the gas content is high, a high flow section is indeedconserved, thereby making it possible to take off the gas effectivelyand consequently to degas the hydrocarbon efficiently. In addition, thetransition between one effective flow section and another takes placewith substantially no inertia since pressure variations in the degassingassembly are transmitted almost instantaneously to the pressure means.

Finally, it will be observed that in the above-mentioned Americanpatent, valve control is performed a posteriori and downstream, since itis necessary for liquid to flow into the degassing vessel in order toclose the valve, whereas in the invention, control of the pressure meanstakes place a priori and upstream, with the degassing system becomingeffective immediately.

In a first embodiment of the invention, said duct-forming means comprisea single duct, and said pressure means comprise, at the end of the ductopening cut into said degassing vessel, Venturi-forming means providedwith a throat, said throat being immersed in the hydrocarbon containedin said degassing vessel, the outlet of said Venturi being disposedabove the hydrocarbon level and being provided with a constriction, saidthroat of the Venturi-forming means being provided with an openingopening out into the hydrocarbon of said degassing vessel, whereby afraction of the mixture flowing along said duct when the gas content ofthe hydrocarbon is high also exits via said opening.

In a second embodiment of the invention, said duct-forming meanscomprise first and second ducts, the open end of the first duct opensout into said degassing vessel, and said pressure means comprise ashutter whereby said second duct opens out into said degassing vessel,and means for controlling closure of said shutter when the gas contentin the hydrocarbon is less than a predetermined value.

In a third embodiment of the invention, said duct-forming means comprisea first duct having a first end connected to said takeoff outlet andhaving its other end connected to Venturi-forming means having a throatand an outlet provided with a constriction located above the hydrocarbonlevel in said degassing vessel, a second duct having a first endconnected to the takeoff outlet and having its other end opening outinto said degassing vessel above the free surface level of thehydrocarbon, and said pressure means comprise a moving shutter for saidduct and control means for said shutter such that the shutter is openwhen the pressure at the throat of the Venturi-forming means is high andsuch that said shutter is closed otherwise.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the present invention appearmore clearly on reading the following description of various embodimentsof the invention given as non-limiting examples. The description refersto the accompanying drawings, in which:

FIG. 1, described above, shows a known degassing system for ahydrocarbon dispenser;

FIG. 2a is a vertical section through a first embodiment of thedegassing system;

FIGS. 2b, 2c, and 2d are detail views showing various embodiments of theVenturi-forming means;

FIG. 3 shows a second embodiment of the degassing system;

FIG. 4 shows a third embodiment of the degassing system;

FIG. 5 is a vertical section through a fourth embodiment of thedegassing system;

FIG. 6 shows a fifth embodiment of the degassing system;

FIG. 7a is an overall vertical section view of a sixth embodiment of thedegassing system; and

FIG. 7b is a view of a detail of FIG. 7a.

DETAILED DESCRIPTION OF THE INVENTION

A first embodiment of the degassing system is initially described, withreference to FIG. 2a. In FIG. 2a, there can be seen the pump 12 with itsnon-return valve 30 and its filter 31 putting into circulation thehydrocarbon which arrives via duct 32 from the storage tank. The outlet33 of the pump is connected to the vortex degassing enclosure 16 andthere can be seen its axial takeoff tube 20 and also the tube 22 forextracting degassed hydrocarbon. The figure also shows a recyclingcircuit 34 provided with a valve 36 which enables excess hydrocarbonflow to be reinserted to the inlet of the pump. There can also be seenin this figure the degassing vessel 24 which includes a valve 37enabling hydrocarbon to be recycled to the inlet of the pump after ithas been degassed in the degassing vessel 24. This structure is wellknown in hydrocarbon dispensers for the purpose of degassing deliveredhydrocarbon.

According to the invention, the takeoff duct 20 is connected to a duct38 which opens out into the degassing vessel 24. More precisely, the end38a of the duct 38 is connected to a Venturi device 40, which Venturidevice has a throat 42 and an outlet 44 opening out above the freeliquid level of hydrocarbon in the vessel 24. This outlet 44 ispreferably provided with a flow rate constriction 46. The throat 42 ofthe Venturi 40 is provided with an opening 48 located beneath theregulated liquid level of hydrocarbon in the vessel 24. According to theinvention, the opening 48 formed in the throat 42 of the Venturi makesit possible to modify the effective flow section of the gas/liquidmixture flowing along the duct 38 as a function of its gas content.

The Venturi 40 with its orifice 48 operates as follows. It is known thata Venturi or Herschel type nozzle is capable of creating a large amountof suction in its throat when it is passing a fluid flow Q_(V) of pureliquid fed by upstream pressure P and opening out to atmosphericpressure P_(O). The absolute pressure in the throat can be close tozero, being limited solely by the vapor pressure of the fluid. Thispressure p at the throat can still remain very low even if aconstriction 46 is placed upstream from the suction generator: theorifice 48 formed in the throat thus enables liquid to be sucked in fromthe vessel.

This sucked-in liquid flow rate q_(V) mixes with the flow rate Q_(V)delivered by the pressure P, and there exists a flow rate q_(V) +Q_(V)to atmospheric pressure. The headloss at the constriction 46 increases,going from a value proportional to Q_(V) ² to a value proportional to(Q_(V) +q_(V))² which has the effect of slowing down the flow rate Q_(V)for given pressure P. Things are quite different when gas is mixed inwith the fluid flow Q_(V) travelling along the nozzle.

Under such circumstances, the relative pressure p at the throat of thenozzle increases rapidly and becomes strongly positive and exceedsatmospheric pressure P_(O) : the flow rate Q_(V) reverses and fluidcontaining air escapes from the throat. Degassing can then take placenot only downstream from the nozzle, but also through the lateralopening in the throat 48, thereby significantly increasing theeffectiveness with which gas is evacuated. In other words, the effectiveoutlet section is reduced when the gas content is zero or very low. Asthe gas content increases, the effective flow section also increases.

The degassing installation shown in FIG. 2a operates as follows: whenthere is no air in the hydrocarbon, a flow rate Q_(V) leaves via theduct 38 and passes through the Venturi 40 before passing into thedegassing vessel. In the absence of any gas, the suction formed at thethroat of the Venturi sucks in a liquid flow rate q_(V), with themixture Q_(V) +q_(V) being expelled into the degassing vessel afterpassing through the constriction 46. The effective flow rate reachingthe degassing vessel is limited to Q_(V) since the flow rate q_(V) doesno more than circulate locally by entering and then leaving the nozzle.The nozzle acts as a circulating pump of flow rate q_(V) and for thispurpose it needs to provide work. Its internal resistance increases andits feed flow rate Q_(V) is reduced.

In contrast, when the flow rate Q_(V) in the duct 38 has a higher gascontent, then the pressure in the throat 42 of the Venturi rises and aflow rate of mixture is expelled not only from the end 44 of theVenturi, but also from the opening 48. Degassing is made much moreeffective by increasing the exhaust section and decreasing the internalresistance of the Venturi 40.

FIG. 2b shows in greater detail the shape of a conventional Venturi 40which, in accordance with the invention, is provided with an orifice 48.

In FIG. 2c, there is shown a Venturi device of the type comprising anozzle followed by a Golaz funnel with an annular vacuum chamber 50 intowhich there opens an orifice 48' that is the equipment of the orifice48. This disposition is strictly equivalent to that of FIG. 2b.

FIG. 2d shows another equivalent of the Venturi device, this equivalentbeing constituted by an injector type nozzle 52 analogous to that usedfor mixing gases that are to be fed to burners. The annular opening 54performs exactly the same function as the orifice 48 or the orifice 48'.

Throughout the description, it should be understood that the term"Venturi device" covers not only a Venturi proper as shown in FIG. 2b,but also nozzle devices of the kinds shown in FIGS. 2c and 2d.

With reference now to FIG. 3, a second embodiment of the degassingdevice is described. In this embodiment, the axial takeoff tube 20 isstill connected to the tube 38 which is provided at its end with aVenturi device 40, the throat 42 of the Venturi device being providedwith an orifice 48. In this embodiment, the axial takeoff tube 20 isalso connected to a second duct 60 whose outlet 62 opens out into thedegassing vessel and can be closed by a moving valve system 64controlled by a deformable membrane 66. The valve control chamber 68defined by the deformable membrane 66 is directly connected to theopening 48 formed in the throat 42 of the Venturi 40. This embodimentoperates as follows. The outlet 44 of the Venturi 40 is provided with aconstriction 46 which makes it possible to limit the flow rate throughthe Venturi to a low value of approximately 1 to 2 liters per minute,for example. If the flow rate Q_(V) flowing along the duct 38 has nogas, then the throat 42 of the Venturi is at low pressure and thedeformable membrane 66 is held in a position such that the movingshutter 64 is closed. The duct 60 is therefore inactive. In contrast,when the duct 38 carries a flow Q_(V) containing gas, the throat 42 ofthe Venturi is at a relatively high pressure which acts on thedeformable membrane 66 to open the shutter 64. The duct 66 is thus madeactive and the total effective flow section is increased.

With reference now to FIG. 4, a third embodiment of the degassing deviceis described. This embodiment is based on the observation that thepresence of air or gas in the hydrocarbon sucked up by the pumpgenerally leads to a decrease in the pressure with which the fuel isdispensed, thereby having the side effect of reducing degassingcapacity. This embodiment takes advantage of this drop in the pressureof the hydrocarbon when it contains air. In this embodiment, there isstill the first duct 38 connected to the axial takeoff tube 20, with thetube 38 terminating in a constriction 70 located above the liquid levelof the hydrocarbon. The second duct 60 also connects the takeoff tube 20to a chamber 72 fitted with a ball valve comprising a ball 74, a seat76, and a return spring 78 tending to move the ball off its seat. Whenthe installation is put under pressure, a jet Q'_(V) is generated in theduct 60, pushing the ball 74 against its seat 76, and compressing thespring 78. Flow along the duct 60 is thus interrupted. If a large amountof gas is sucked in, thereby causing the pressure to drop beneath acertain value, and in particular the pressure in the duct 60, then thespring 76 moves the ball away from its seat, thus enabling a permanentdegassing flow to be established in the duct 60 in addition to the flowin the duct 38. This considerably improves degassing preformed by thevortex degasser 16.

Another method of increasing the effectiveness of degassing is shown inFIG. 5. Advantage is taken of the almost constant flow rate generated bythe pump 12 when there is no air in the fuel, giving rise to a headlossΔp that varies little at the outlet of the pump 33 at a location wherethe fluid is subjected to a sudden change in flow profile. This occurs,in particular, at the inlet to the vortex degasser 16 which causes thefluid to enter the tube 5 tangentially for centrifuging to take place.

The constant flow rate Q of the pump 12 is ensured at all times becauseof the regulation provided by the return valve 36.

Since headloss Δp is proportional to the product of fluid density ρmultiplied by the square of its flow rate Q, Δp =KρQ², any intake of aircauses the density ρ to fall off quickly and also the flow rate Q, thusleading to a rapid drop in Δp. This variation Δp generated across twopressure takeoffs situated on either side of the inlet 33 of the vortextube 16, for example, is directed via two ducts 80 and 82 to a membranesensor 84 carrying a valve member 86. The valve 86 can vary the flowsection of the auxiliary degassing channel 60' through which a flowQ'_(V) can be added to the continuous flow Q_(V) flowing along the mainchannel 38 which is provided at its end 14 with a constriction 70 thatgreatly limits Q_(V).

In the absence of air, the high value of Δp closes the valve 86 andQ'_(V) =0. From a predetermined value of air sucked into the pump andpassing through the vortex inlet 33, the valve 86 is opened and Q'_(V)≠0, thereby increasing the effective flow sections for exhausting gasvia the channel 38.

In all of the above, steps have been made to increase degassingeffectiveness of hydrocarbon dispensers by creating additional flowsection for exhausting air before the substance delivered to thecustomer begins to contain a quantity of gas that exceeds the limitslaid down by regulations. It is also possible to provide for auxiliarydegassing only when gas becomes manifest in fuel that has been subjectedto insufficient degassing due to the separator elements becomingsaturated. It is thus possible to analyze the fluid that has beenconveyed to the outlet 22, 34 of the degasser 16 and which cannotlegally contain more than 0.5% or 1% gas, depending on the nature of thefuel. This analysis can be performed, for example, in the zone 90upstream from the valve 36 in the recycling duct 34 which alsoconstitutes the outlet duct 22 for taking "degassed" hydrocarbon fromthe vortex degasser 16.

FIGS. 6 and 7a show two embodiments of a degassing system based on thisprinciple.

In the embodiment of FIG. 6, the axial takeoff duct 20 is connectedfirstly to the duct 38 provided with its constriction 70, and secondlyto the auxiliary duct 60 whose end 60a is provided with a valve 92controlled by movement of a deformable membrane 94. The position of themembrane 94 and thus the state of the valve 92 is controlled by thepressure which obtains in a control chamber 96.

In the zone 90, a duct 98 allows a permanent flow to take place towardsthe degassing vessel 24. The end 98a of the duct 98 is disposed abovethe liquid level of hydrocarbon in the vessel 24 and is directed upwardsto form a fluid jet 100. This jet 100 is directed towards a recoverynozzle 102 connected to the control chamber 96. This nozzle generates adynamic pressure which is applied to the membrane 94. The valve 92 openswhen the dynamic pressure of the jet becomes insufficient, allowing anadditional degassing flow to take place via the auxiliary duct 60.

In the embodiment of FIG. 7a, the duct 38 connected to the axial takeoffduct 20 of the vortex degasser 16 includes a small-section parallel duct60" whose end 60"a opens out into the degassing vessel 24. The end 38aof the duct 38 is connected to a slide valve 110. The valve 110 has anoutlet 112 located in the vessel 24 above the liquid level ofhydrocarbon in the vessel. The slide 114 of the valve 110 is controlledby pressure applied to its end face 114a, with its other end face 114bbeing subjected to the action of a return spring 116. A duct 118 putsthe zone 90 of the outlet 22, 34 of the degasser 16 into permanentcommunication with the control chamber 134 of the slide valve 110defined by the end 114a of the slide. Thus, the pressure which obtainsin the zone 90 is permanently applied to the end face 114a of the valveslide.

When this pressure is high in the zone 90, the slide 114 is pushed backand compresses the spring 116. In this position, the slide 114interrupts communication between the inlet 38a and the outlet 112 of thevalve. Only the duct 60" allows liquid to escape into the vessel 24. Incontrast, when the pressure in the zone 90 is lower, then the slide 114occupies the position shown in FIG. 7a and the liquid/gas mixture canalso leave via the valve 110, thereby naturally increasing the effectivedegassing flow section.

FIG. 7b shows a preferred embodiment of a portion of the apparatus showndiagrammatically in FIG. 7a. The valve 110 is constituted by a body 120having an inlet opening 122 connected to the end 38a of the duct 38, andit also has an outlet opening 124. The slide 114 has an annular opening126 making it possible in certain positions of the slide to put theinlet into communication with the outlet. An orifice 128 opening outdirectly into the vessel 24 constitutes the equivalent of the duct 60".In the body 120 of the valve, there is mounted a return spring 130 whichacts on a shoulder 132 of the slide. The control chamber 134 of theslide is directly connected to the zone 90 by a screw 136 having bores138 and 140. The screw 136 constitutes the equivalent of the duct 118 inFIG. 7a.

We claim:
 1. A degassing system for a hydrocarbon dispenser having apump (12) for making hydrocarbon flow, said system comprising adegassing assembly (16) having an inlet (33) connected to the outlet ofthe pump, and a degassed hydrocarbon outlet (22), and a takeoff outlet(20) for taking off a hydrocarbon/gas mixture, a degassing vessel (24),and duct-forming means (38, 60, 60') for connecting said takeoff outlet(20) to said degassing vessel, the system being characterized in thatsaid duct-forming means includes a first duct (38) and a second duct(60, 60') both opening out into said degassing vessel (24), the openingout end of said second duct (60, 60') having a flow section that isadjustable, and in that said degassing system further includes adjustingmeans (64, 74, 84, 92) capable of modifying said flow section as afunction of the gas content of the hydrocarbon so that said sectionincreases when the gas content increases, wherein said adjusting meanscomprise a shutter (64, 74, 86) whereby said second duct (60) opens outinto said degassing vessel, and means (66, 72, 84) for controllingclosure of said shutter when the gas content in the hydrocarbon is lessthan a predetermined value, and wherein said adjusting means comprise,at the end of the second duct (60) opening out into said degassingvessel (24), a rated ball valve (72, 74, 76) such that in the absence ofgas in the hydrocarbon, the valve is closed and, for a gas contentexceeding a predetermined value, said valve is open under the effect ofvariations in the pressure of the fluid flowing along the second duct(60).
 2. A degassing system for a hydrocarbon dispenser having a pump(12) for making hydrocarbon flow, said system comprising a degassingassembly (16) having an inlet (33) connected to the outlet of the pump,and a degassed hydrocarbon outlet (22), and a takeoff outlet (20) fortaking off a hydrocarbon/gas mixture, a degassing vessel (24), andduct-forming means (38, 60, 60') for connecting said takeoff outlet (20)to said degassing vessel, the system being characterized in that saidduct-forming means includes a first duct (38) and a second duct (60,60') both opening out into said degassing vessel (24), the opening outend of said second duct (60, 60') having a flow section that isadjustable, and in that said degassing system further includes adjustingmeans (64, 74, 84, 92) capable of modifying said flow section as afunction of the gas content of the hydrocarbon so that said sectionincreases when the gas content increases, wherein said adjusting meanscomprise a shutter (64, 74, 86) whereby said second duct (60) opens outinto said degassing vessel, and means (66, 72, 84) for controllingclosure of said shutter when the gas content in the hydrocarbon is lessthan a predetermined value, and wherein the outlet of said pump (12)includes constrictions (33) on either side of which a pressuredifference is established that is representative of the gas content ofthe hydrocarbon at the outlet from said pump, the system beingcharacterized in that said adjusting means comprise, at the end of thesecond duct (60') opening out into said degassing vessel (24), a valve(86) controlled by the displacements of a differential pressure sensor(84) and means (80, 82) for applying the pressure difference that existson either side of said constrictions to said differential pressuresensor.
 3. A system according to claim 2, characterized in that saiddifferential pressure sensor is a deformable membrane (84) which issubjected to said pressure difference.